Hemodialysis Systems and Methods

1. A hemodialysis system, comprising: a blood flow path through which untreated blood is drawn from a patient and passed through a dialyzer; a dialysate flow path through which dialysate flows from a dialysate supply through the dialyzer, the dialysate flow path and the blood flow path being in fluidic communication; a reciprocating positive displacement blood pump configured to pump blood in the blood flow path, resulting in blood flow through the dialyzer; a reciprocating positive displacement dialysate pump configured to pump dialysate in the dialysate flow path, resulting in dialysate flow through the dialyzer; and a controller configured to receive pressure information associated with the blood flow path and/or pressure information associated with the dialysate flow path, and configured to control the dialysate pump and/or the blood pump; wherein the controller uses the pressure information during dialysis to control the dialysate pump and/or the blood pump such that the pressure of the dialysate exiting the dialyzer is lower than the pressure of the blood exiting the dialyzer.

2. The hemodialysis system of claim 1 , wherein the blood flow path comprises a blood flow cassette.

3. The hemodialysis system of claim 1 , wherein the dialysate flow path comprises at least one cassette.

4. A hemodialysis system, comprising: a blood flow path through which untreated blood is drawn from a patient and passed through a dialyzer; a dialysate flow path through which dialysate flows from a dialysate supply through the dialyzer, the dialysate flow path and the blood flow path being in fluidic communication; a reciprocating positive displacement blood pump configured to pump blood in the blood flow path, resulting in blood flow through the dialyzer; a reciprocating positive displacement dialysate pump configured to pump dialysate in the dialysate flow path, resulting in dialysate flow through the dialyzer; and a controller configured to receive pressure information associated with the blood flow path and/or pressure information associated with the dialysate flow path, and configured to control the dialysate pump and/or the blood pump; wherein the controller uses the pressure information during dialysis to control the dialysate pump and/or the blood pump device such that the pressure of the dialysate entering the dialyzer is greater than the pressure of the blood entering the dialyzer.

5. The hemodialysis system of claim 4 , wherein the blood flow path comprises a blood flow cassette.

6. The hemodialysis system of claim 4 , wherein the dialysate flow path comprises at least one cassette.

7. The hemodialysis system of claim 1 , wherein the controller is configured to detect when the blood pump is not delivering blood to the dialyzer, and is configured to prevent or stop delivery of dialysate by the dialysate pump during this time.

8. The hemodialysis system of claim 1 , further comprising a second reciprocating positive displacement dialysate pump, the second dialysate pump configured to receive dialysate exiting the dialyzer, and the first dialysate pump configured to deliver dialysate to the dialysate flow path, wherein the controller is configured to control the dialysate pumps or the blood pump to ensure that a pumping chamber of the second dialysate pump is completely filled with dialysate exiting the dialyzer during a fill stroke of the second dialysate pump.

9. The hemodialysis system of claim 4 , wherein the controller is configured to control the dialysate pump or the blood pump to ensure that the dialysate pump delivers a complete pump stroke to the dialysate flow path during a delivery stroke of the dialysate pump.

10. The hemodialysis system of claim 1 , wherein the dialyzer comprises a blood flow side comprising a blood flow inlet and blood flow outlet in fluid communication with the blood flow path, and a dialysate flow side in fluid communication with the dialysate flowpath, and wherein the blood flow side of the dialyzer is separated from the dialysate flow side of the dialyzer by a semi-permeable membrane; the blood pump is configured to pump blood in the blood flow path, resulting in blood flow through the dialyzer from the blood flow inlet of the dialyzer to the blood flow outlet of the dialyzer; the dialysate pump is configured to pump dialysate in the dialysate flow path, resulting in dialysate flow through the dialyzer from the dialysate flow inlet of the dialyzer to the dialysate flow outlet of the dialyzer; and wherein the controller is configured to control the dialysate pump and/or the blood pump such that the pressure of the dialysate exiting the dialyzer via the dialysate flow outlet is lower than the pressure of the blood exiting the dialyzer via the blood flow outlet.

11. The hemodialysis system of claim 4 , wherein the controller is configured to detect when the blood pump is not delivering blood to the dialyzer, and is configured to prevent or stop delivery of dialysate by the dialysate pump during this time.

12. The hemodialysis system of claim 4 , wherein the dialyzer comprises a blood flow side comprising a blood flow inlet and blood flow outlet in fluid communication with the blood flow path, and a dialysate flow side in fluid communication with the dialysate flowpath, and wherein the blood flow side of the dialyzer is separated from the dialysate flow side of the dialyzer by a semi-permeable membrane; the blood pump is configured to pump blood in the blood flow path, resulting in blood flow through the dialyzer from the blood flow inlet of the dialyzer to the blood flow outlet of the dialyzer; the dialysate pump is configured to pump dialysate in the dialysate flow path, resulting in dialysate flow through the dialyzer from the dialysate flow inlet of the dialyzer to the dialysate flow outlet of the dialyzer; and wherein the controller is configured to control the dialysate pump and/or the blood pump such that the pressure of the dialysate exiting the dialyzer via the dialysate flow outlet is lower than the pressure of the blood exiting the dialyzer via the blood flow outlet.